This invention relates to the recovery of copper values from cupric ion-containing ammoniacal solutions thereof, to the recovery and regeneration of spent printed circuit board etchant, and to ion-exchange media useful in such recoveries.
Extraction of metallic ions from aqueous solutions by ion exchange and solvent extraction with liquid complexing agents is known. There have been consistent problems in the art, however, with low selectivity and fouling of the aqueous effluent by the complexing agents, in some cases requiring further treatment of the effluent with chelating agents, and in others with adsorbent material.
Attempts have been made to immobilize the liquid complexing agents in solid porous media, but these have been subject to the same drawbacks. See, for example, Hughes et al. Trans. Inst. Min. Metall. 85 (1976) C123 which discloses the removal of cupric ion from an aqueous solution with the liquid ion-exchange complexing agent LIX 64N adsorbed onto an expanded polyurethane foam. Warshawsky, in Trans. Inst. Min. Metall. 83 (1974) C101 discloses the removal of copper ions with LIX 64N adsorbed into polymeric adsorbents of the XAD series. In South African Pat. No. 70/4209 to Lloyd, there is disclosed the removal of copper, gold and uranium with ion-exchange materials comprising clays impregnated with various ion-exchange compounds. An activated charcoal substrate for the complexing agents salicylaldoxime and benzolylacetone for the removal of copper, cobalt, nickel and iron from zinc sulphate solutions is disclosed in Moore U.S. Pat. No. 3,682,589. There are three major disadvantages of such porous supports. One is that they entrain feed solutions and so require a great deal of rinsing, which reduces the efficiency and selectivity of the extraction process. Another is that the liquid complexing agent is lost from the porous support rather rapidly. Finally, agent-filled supports in flat-sheet membrane and hollow-fiber membrane forms withstand only minimal pressure differentials, on the order of 10 psi or less, without agent being forced out of the pores, which restricts their use to low-pressure operations.
The industrial use of ammonia-containing solutions for the dissolution of copper and certain copper-containing materials is widespread. For example, the printed circuit board industry uses an alkaline ammonia etching process to remove unwanted copper from selected areas of printed wiring boards. This industry consumes about 9,000,000 gallons of ammonia etching solution annually which contains approximately 1.5 lb/gal of NH.sub.3 in the form of free ammonia and ammonia salts and about 1.3 lb/gal of dissolved copper in the form of cupric (2+) ion. Typical printed circuit board etchants comprise a buffered ammoniacal solution with a pH of from 8 to 12 which may contain about 0.1 to about 1.0% by weight additives such as wetting and banking agents. Ammonia-containing solutions are also used by the mining industry for the leaching of copper values from certain copper-containing ores.
Copper metal cannot be recovered directly from these ammoniacal cupric ion-containing solutions. In the case of ammoniacal printed circuit board etchants, once the copper concentration reaches about 160 g/L the solution is considered spent and is either discarded or returned to the manufacturers. Copper is often recovered by the etchant manufacturer by raising the pH of the spent etchant and boiling off the ammonia, thus allowing copper to precipitate as the oxide.
Solvent extraction using selective liquid ion-exchange agents has also been suggested for the extraction of copper from such ammoniacal etch solutions. See, for example, U.S. Pat. Nos. 4,083,758, 4,252,621, and 4,350,667. In such solvent extraction processes the ammoniacal copper solution is intimately contacted with an organic liquid ion-exchange material that selectively extracts copper ions. A phase separation must then be performed to remove the copper-containing organic liquid from the aqueous ammoniacal solution. Copper is then removed from the loaded organic liquid ion-exchange agent by contact with an aqueous acid solution (such as sulfuric acid) which strips the copper from the organic ion-exchange agent. A second phase separation must then be performed to separate these aqueous and organic liquids.
Such prior art liquid-liquid phase separation steps in the solvent extraction process are cumbersome and require expensive and complex equipment. As disclosed in U.S. Pat. No. 4,252,621, in the case of ammoniacal printed circuit board etchant regeneration, it is essential that no organic ion-exchange agent remain in the etchant solution as this material could contaminate the surface of the printed wiring boards, causing serious complication in subsequent processing steps. Therefore, not only must the liquid-liquid separation steps be closely and carefully controlled, but the etchant solution must also be carbon filtered to remove the last traces of organic ion-exchange agent before becoming useable again.
The use of solvent extraction techniques by the mining industry for the recovery of copper from ammonia leach solutions involves extensive liquid-solid separations along with liquid-liquid separations. After the finely ground ore is contacted with the ammonia leach solution, as many as five separate liquid-solid separation steps may be required. Finally, the leach solution must be filtered to insure that no particulates are present onto which the organic liquid ion-exchange agent may adsorb in the solvent extraction stage. Solvent extraction is then performed on the filtered leach solution in stages. To insure the most efficient recovery of copper from the ammonia leach in such processes, several extractions are performed, each of which reduces the copper concentration to a successively lower level until nearly all the copper has been extracted. The extraction solutions are then combined and washed at least once with water to remove any entrained leach solution. Each extraction and wash stage requires its own liquid-liquid separation equipment. The loaded liquid ion-exchange agent must then be stripped of its copper content, which again requires additional liquid-liquid separation equipment.
It is apparent from the foregoing that there is a great need in the ammoniacal copper recovery art for a simple and inexpensive ion-exchange method that may be accomplished without extensive liquid-liquid separations and with ion-exchange media that have superior agent retention, a long life, and are reuseable. These and other objects are accomplished by the present invention, which is summarized and more particularly described below.